Abstract

This work is the beginning of a study on the fossil fauna complex denominated "Mesopotamiense", lower strata of the Paraná cliffs (Province of Entre Ríos) assigned to the upper Pliocene. A brief description is given of the origin of the "Entre Ríos Formation" followed by a redescription and discussion on morphological dental characteristics of the Proterotheriinae (Mammalia, Litopterna ), group studied by Ameghino. Each genus is compared with examples recorded under other Argentina Terciary formations establishing the existente of typical genus of the Upper Miocene (Santacrucense Age ) and the Upper Pliocene (Montehermosense Age ) in the "Mesopotamiense".